In recent years, various research and development of a display device including a thin film transistor (TFT) device have been conducted. Since this TFT is excellent in low power consumption and space-saving, it has been increasingly used as a transistor for driving a display device of a portable device such as a mobile phone, a notebook computer, or a PDA. Most of the TFTs mentioned above are fabricated from an inorganic semiconductor material such as crystalline silicon or amorphous silicon. This is because such a TFT can be fabricated by using conventional manufacturing process and manufacturing technology for a semiconductor device. In a case of using the manufacturing process of a semiconductor device, however, since a processing temperature in forming a semiconductor film reaches 350° C. or higher, a substrate on which the TFT can be formed is limited. In particular, since many flexible substrates such as a plastic substrate have the heatproof temperature of less than 350° C., it is difficult to use such a flexible substrate for the fabrication of a TFT made of an inorganic semiconductor material according to the usual semiconductor manufacturing process.
For the solution of this problem, recently, research and development of a TFT device using an organic semiconductor material (hereinafter, abbreviated to organic TFT) which can be fabricated at low temperature have been conducted. Since an organic semiconductor film of the organic TFT can be formed at low temperature, it is possible to form the organic TFT on a substrate with low heat resistance such as a plastic substrate. Therefore, it becomes possible to fabricate a novel device with a nonconventional flexibility.
As a method for forming an organic semiconductor film in forming an organic TFT, depending on the organic semiconductor material to be used, an optimal method has been used from among a printing method such as an ink jet, a spin-coating method, a spraying method, a transfer method, a deposition method, a dipping method, a casting method, and the like. For example, a low molecular compound such as pentacene derivatives is mainly formed by the deposition method, and a high molecular compound such as polythiophene derivatives is formed from a solution. As an example related to a method for manufacturing a semiconductor device including an organic thin film transistor, Japanese Patent Application Laid-Open Publication No. 2004-080026 (Patent Document 1) is known. This example has disclosed a technique for suppressing the usage of an organic semiconductor material by the use of the capillarity.
Recently, research and development for achieving the price reduction by fabricating a channel portion of a TFT from a small amount of an organic semiconductor material without wasting the organic semiconductor material by using a printing process such as an ink jet, a micro-dispensing, or a transfer method have been conducted. In addition, research and development for fabricating an electrode and a wiring portion by printing are beginning to be conducted.